Registering of motor to get the rewards when filling up at Engen

A recent message from FNB instructs me to register my motor vehicle on their app in order to get the eBucks when filling up at an Engen petrol station. This is ridiculous, if I want to fill up my mother's car and pay with my FNB card, I should be able to do it and still earn eBucks. It just feels like too much control - they have no business with my motor vehicles and I would like to hear from them ONE good reason why this is necessary. Everything becomes so complicated, I seriously consider moving my assets to another bank.